A typical gas turbine engine includes a fan, compressor, combustor, and turbine disposed along a common longitudinal axis. Fuel and compressed air discharged from the compressor are mixed and burned in the combustor. The resulting hot combustion gases (e.g., comprising products of combustion and unburned air) are directed through a conduit section to a turbine section where the gases expand to turn a turbine rotor. In electric power applications, the turbine rotor is coupled to a generator. Power to drive the compressor may be extracted from the turbine rotor.
The one or more conduits forming the conduit section are liners or transition ducts through which the hot combustion gases flow from the combustion section to the turbine section. Due to the high temperature of the combustion gases, the conduits must be cooled during operation of the engine in order to preserve the integrity of the components. Commonly, the combustor and turbine components are cooled by air which is diverted from the compressor and channeled through the components.
Known solutions for cooling the conduits include supplying the cool air along an outer surface of the conduit to provide direct convection cooling to the transition duct. An impingement sleeve may be provided about the outer surface of the conduit to facilitate flow of the cooling fluid, e.g., through small holes formed in an impingement member before the air is introduced to the outer surface of the conduit. Other prior art solutions include injecting the cooling fluid along an inner surface of the conduit to provide film cooling along the inner surface.
Effective cooling of turbine components, e.g., airfoils, must deliver the relatively cool air to critical regions such as along the trailing edge of a turbine blade or a stationary vane. The associated cooling apertures may, for example, extend between an upstream, relatively high pressure cavity and one of the exterior surfaces of the turbine blade. It is a desire in the art to provide cooling designs and methods which provide more effective cooling with less air. It is also desirable to provide more cooling in order to operate machinery at higher levels of power output. Generally, cooling schemes should provide greater cooling effectiveness to create more uniform wall temperatures along the components.
Ineffective cooling can result from poor heat transfer characteristics between the cooling fluid and the material to be cooled with the fluid. In many cases, it is desirable to establish film cooling along a wall surface. A cooling air film traveling along the surface of a wall can be an effective means for increasing the uniformity of cooling and for insulating the wall from the heat of hot core gases flowing thereby. However, film cooling is difficult to maintain in the turbulent environment of a gas turbine.
Also, gaps which exist between apertures and in areas immediately downstream of the gaps, are exposed to less cooling air than are the apertures and the surface areas immediately downstream of the apertures. Consequently these regions are more susceptible to thermal degradation.